Field of Invention
The present invention relates to tool steel, and more particularly to a powder metallurgy wear-resistant tool steel.
Description of Related Arts
Tool steel is widely used in manufacturing field. For a long service life of a tool made of the tool steel, the tool steel should be sufficient in wear resistance, impact toughness, bending strength and hardness. Under normal conditions of use, wear resistance determines the length of service life. Wear resistance of the tool steel depends on the matrix hardness, as well as content, morphology and particle size distribution of the second hard phase in the steel. The second hard phase in the steel comprises M6C, M2C, M23C6, M7C3 and MX carbides, wherein microhardness of the MX carbides are higher than other carbides, for providing better matrix protection during operation, thereby reducing wear and improving the service life of molds. Impact toughness and bending strength are key indicators of toughness. Coarse carbides in the steel will cause stress concentration, which reduces the toughness of the tool steel, resulting in fracture under a relatively low external load. In order to improve the toughness of the tool steel, it is important to reduce or refine the carbides. In order to avoid plastic deformation, hardness of the tool steel is usually required to be HRC60 or more.
Conventionally, the tool steel is mainly casted and forged by traditional production processes, wherein the tool steel prepared by casting and forging processes is limited by liquid steel which is slowly cooled during the processes. As a result, alloy components are easy to be segregated during consolidation and to form the coarse carbides. Even after subsequent forging and rolling processes, such bad structure will still adversely affect the performance of the alloy, resulting in low performances of the tool steal in strength, toughness, wear resistance and grinding performance, which is difficult to meet material performance and life stability requirements of high-end manufacturing. Tool steel prepared by a powder metallurgy method avoids the segregation problem of alloy elements, wherein the powder metallurgy method mainly comprises steps of: preparing powder by atomization, and forming the powder by consolidation. In the step of preparing powder by atomization, liquid steel is rapidly cooled into powder. Therefore, the alloy elements in the liquid steel are completely consolidated before segregation. A structure is fine and even after powder consolidation, wherein compared with casting and forging, alloy performance is significantly improved. Conventionally, only the powder metallurgy method is able to satisfy extremely high performance requirements of high alloy tool steel. Tool steel prepared by powder metallurgy has been reported, but components of some kinds of steel are not reasonably designed, so structure and performance should be further improved.